I think id be hesitant with crustaceans. The shrimp big enough to survive the nagging and nipping and chomping of the cichlids are generally big enough to do an awful lot of damage to the cichlids when they get hold of them.
Otherwise.. i love the Giant River Prawns (Macrobrachium rosenbergii). Though these devil make your average psychopath seem cute and cuddly! I didnt realise how psychotic and aggressive they were! And yet so very very cool!
They eat each other... let alone anything else unlucky enough to be near them!
http
/www.google.co.uk/imgres?q=macrobrachium+rosenbergii&um=1&hl=en&sa=N&biw=1059&bih=607&tbm=isch&tbnid=GRdFPSbR-i-B1M:&imgrefurl=http
/commons.wikimedia.org/wiki/File:Washington_DC_Zoo_-_Macrobrachium_rosenbergii_4.jpg&docid=H_sVCxs1xerVLM&imgurl=http
/upload.wikimedia.org/wikipedia/commons/f/f6/Washington_DC_Zoo_-_Macrobrachium_rosenbergii_4.jpg&w=3872&h=2121&ei=oStAT73-Eqay0QWosoiPDw&zoom=1&iact=hc&vpx=604&vpy=155&dur=278&hovh=166&hovw=304&tx=148&ty=100&sig=103349512573384008980&page=1&tbnh=91&tbnw=166&start=0&ndsp=15&ved=0CE8QrQMwAw
As for plecs... I like nice L numbers, i dont need fancy.. nice will do!
I like the Sabaji Plec (mine grew to about 22cm before i had to rehome him when i broke down tank)
http
/www.google.co.uk/imgres?q=sabaji+pleco&hl=en&biw=1059&bih=607&gbv=2&tbm=isch&tbnid=ZYHGwUb_9b8RAM:&imgrefurl=http
/www.aquahobby.com/gallery/e_Peckoltia_sabaji.php&docid=sO07TYgouiW4rM&imgurl=http
/www.aquahobby.com/gallery/img/Peckoltia_sabaji_2.jpg&w=630&h=300&ei=FSxAT_GSPKPD0QW3uLyPDw&zoom=1&iact=hc&vpx=537&vpy=181&dur=35&hovh=155&hovw=326&tx=144&ty=79&sig=103349512573384008980&page=1&tbnh=71&tbnw=149&start=0&ndsp=17&ved=0CFIQrQMwAw
Or Triactis plecs
http
/www.google.co.uk/imgres?q=triactis+plec&hl=en&gbv=2&biw=1059&bih=607&tbm=isch&tbnid=__IiMi0OkUJgjM:&imgrefurl=http
/www.planetcatfish.com/cotm/cotm.php%3Farticle_id%3D140&docid=VrT5vrBgyPDWmM&imgurl=http
/www.planetcatfish.com/images/full/loricariidae/leporacanthicus/triactis/1.jpg&w=800&h=456&ei=nixAT66RA-am0QWD_vyPDw&zoom=1&iact=rc&dur=235&sig=103349512573384008980&page=1&tbnh=96&tbnw=169&start=0&ndsp=15&ved=0CFEQrQMwBA&tx=161&ty=32
Blue Phantom
http
/www.google.co.uk/imgres?q=blue+phantom+pleco&hl=en&gbv=2&biw=1059&bih=607&tbm=isch&tbnid=5uoxRCwf0ewrXM:&imgrefurl=http
/bubblesaquarium.com/fish_Plecos.htm&docid=eCqwIdq-kLSDAM&imgurl=http
/bubblesaquarium.com/images/Fish/Plecos/Spotted_L128_Pleco.jpg&w=300&h=160&ei=0SxAT5HYM4Ow0QWiqJWPDw&zoom=1&iact=rc&dur=368&sig=103349512573384008980&page=1&tbnh=76&tbnw=143&start=0&ndsp=17&ved=0CFUQrQMwBA&tx=79&ty=50
Flash Plec
http
/www.google.co.uk/imgres?q=L204+pleco&hl=en&gbv=2&biw=1059&bih=607&tbm=isch&tbnid=lPSuNLSUyS9GeM:&imgrefurl=http
/www.planetcatfish.com/cotm/cotm.php%3Farticle_id%3D307&docid=6V2lkcdbp6gtPM&imgurl=http
/www.planetcatfish.com/images/full/loricariidae/panaque/sp(l204)/1.jpg&w=640&h=444&ei=Xy1AT5LmMuW80QXP9PSPDw&zoom=1&iact=rc&dur=143&sig=103349512573384008980&page=1&tbnh=126&tbnw=168&start=0&ndsp=15&ved=0CFEQrQMwBA&tx=99&ty=90
And one of my favourites but was generally always out of my budget at the time i saw them. Though did have 3 a few years back!
Scobiancistrus aureatus (Goldie Pleco/Sunshine Plec)
http
/www.google.co.uk/imgres?q=scobinancistrus+aureatus&hl=en&gbv=2&biw=1059&bih=607&tbm=isch&tbnid=f3UgNxRf7RenCM:&imgrefurl=http
/www.l-welse.com/reviewpost/showproduct.php/product/23&docid=AU0B0ax2yvhnEM&imgurl=http
/www.l-welse.com/gallery/files/9/1/3/scobinancistrus_aureatus_l_14_bild01_850.jpg&w=850&h=567&ei=3y1AT53UOamk0QWh7IyPDw&zoom=1&iact=rc&dur=99&sig=103349512573384008980&page=2&tbnh=132&tbnw=172&start=15&ndsp=20&ved=0CJUBEK0DMBM&tx=115&ty=59
Im not fussed with all these poncy little Golden Nuggets that hang around the 10-12cm mark, i preferred the larger, slightly more aggressive (or can at least stand up for itself!) plec that would rather eat a bit of prawn or mussel (what my cichlids often ate) than the algae which i got ancistrus to eat.
Though that said, i had Tambo Ancistrus... lovely things
http
/www.google.co.uk/imgres?q=tambo+ancistrus&hl=en&sa=X&gbv=2&biw=1059&bih=607&tbm=isch&tbnid=8KKI1ChjVeUE8M:&imgrefurl=http
/www.hippocampus-bildarchiv.com/tier_2992_L089Ancistrussp.(tamboensis%3F).htm&docid=F3p4AL3rk4RAFM&imgurl=http
/www.hippocampus-bildarchiv.com/images/S43089_L089Ancistrus_sptamboensis.jpg&w=418&h=283&ei=gy5AT9qGEejB0QXPzJmPDw&zoom=1
Oscars are nosey and incredibly stupid. The shrimp might be bigger than them and they would still pick at it and kill it.... leg by leg if they had to.
And I've seen oscars buch much bigger than 14"